Methods for preparing a low water permeability, edible film

ABSTRACT

Disclosed are edible film coating compositions of low moisture permeability and their methods of preparation. The compositions comprise cross-linked, refined shellac and preferably an edible member having a reactive hydroxyl or acid moiety selected from the group consisting of edible sources of polyphenolics, edible sources of benzaldehyde and derivatives, acetylated monoglycerides, polyglycerol esters, edible straight chain mono-carboxylic acid, edible di-carboxylic acids and mixtures thereof. Useful weight ratios of shellac to reactant range from 1:0.001 to 0.1. In the preferred method of preparation, the shellac is cross-linked with the reactants in a dry, molten mixture by heating at 130° to 175° C. for 2 to 15 minutes. The resulting coating compound while molten is dissolved in a food grade solvent, applied to a substrate and dried. The coating compositions are particularly useful as a moisture barrier in composite food articles having phases in contact which differ substantially in water activity. Effective films range from 0.1 to 5 mils in thickness.

This is a division of application Ser. No. 788,178, filed Oct. 16, 1985,now U.S. Pat. No. 4,710,228.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to food products and to their methods ofpreparation. More particularly, the present invention relates to ediblefood coating compositions comprising cross-linked shellac and certainselected edible reactants and to their methods of preparation.

2. The Prior Art

Although the coating of food to protect such food against oxidativedegradation, mold attack, and moisture penetration is well known, mostcoatings employed for such purposes are not edible and must be removedbefore the food can be consumed. If the coating employed adheres well tothe the food product, the removal of such coating can be difficult andtime consuming. Additionally, if the food product is brittle andfragile, the food product can break during the stripping of the coating,making the consumption of the food difficult and resulting in the lossof the food product. An edible food coating which does not requireremoval prior to consumption of the food product and which affords thenecessary protection, particularly against moisture penetration, istherefore highly desirable.

A particular problem exists in the protection of food products withedible coatings or barriers with respect to composite foods comprisingphases of dissimiliar materials, e.g., ice cream sandwiches or cheeseand crackers, whose composite phases may differ in such properties aswater activity, acidity, protein level and the like. Due to the variousgradients in water activity and the like between the phases as well asthe physical contact, migration and/or diffusion of species between thephases can occur which can result in degradation of the properties ofeach phase. For example, moisture may migrate from the cheese to thecracker undesirably drying the cheese and at the same time undesirablyreducing the crispness of the cracker. Furthermore, removal of anyintermediate barrier material can be quite inconvenient.

Among the various potential gradients in such composite food articles,moisture migration remains the most significant problem area. Whilethroughout the remainder of the specification below, particularattention is addressed to the problems of moisture migration andmoisture penetration of coating or barrier compositions, the skilledartisan will appreciate that the present invention also finds usefulnessin the problems associated with additional migration or penetrationproblems including oxygen, acidity, color, oil and protein.

In the past, the art has attempted to prepare composite food articles byformulating the different food phases so that the water activity of thephases were approximately the same so as to minimize moisture migration.However, not only does this limit the range of composite food productspossible, but moisture migration problems remain nonetheless. Oneapproach towards providing an edible, low water permeable barrier hasbeen to formulate barriers based upon compound fats (see U.S. Pat. No.4,396,633, issued Aug. 2, 1983 to D. Tresser) or with formed in-situ gelmembrane (see U.S. Pat. No. 4,401,681, issued Aug. 30, 1983 to Dahle).However, such barrier or coating compositions suffer from numerousdisadvantages. Among the problems is that in order for compound fatcoatings or barriers to be effective over long periods of time, the fatcoats must be relatively thick. Additionally, especially with regard tochilled or frozen food articles, the fat barriers become relativelybrittle at those reduced temperatures. Fissures or cracks may occurbreaching the integrity of the barrier and allowing moisture migrationto occur. Also, the fat coatings may be organoleptically undesirableproviding a noticeable presence in an undesirably waxy mouthfeelespecially at reduced consumption temperatures.

The prior art additionally includes attempts at providing edible coatingcompositions of low water permeability which are effective as relativelythin films. Coating compositions based upon modified methyl or ethylcellulose ether are known (see U.S. Pat. No. 3,471,304 and U.S. Pat. No.3,471,303, each issued Oct. 7, 1969 to M. M. Handy et al.).Additionally, coating compositions based upon shellac are also known(see U.S. Pat. No. 3,741,795, issued June 26, 1973 to C. A. Signorino).However, the compositions of each of these two references suffer fromseveral disadvantages. First, each of the food compositions, whiledesignated as edible, typically include ingredients which are notapproved by the Food and Drug Administration. Additionally, while thecoating compositions do provide a measure of water impermeability,further improvements in this important attribute are desirable. Also,the '304 patent teaches the necessity of employing both acylated fattyglycerides and certain metal salts.

This invention is suitable for commercial operations and providescompositions which have improved properties in the edible food coatingfields. The compositions of the present invention may be prepared in theform of pre-polymerized or baked on films depending on the heattolerance properties of the substrate coated. After air drying or curingthe film possesses excellent oil, water and aging resistance and unusualtoughness and elasticity or flexibility. Various other outstandingproperties will be apparent from the following description of thecompositions of the present invention disclosures.

When small molecules permeate through a polymer membrane, the rate ofpermeation can be expressed by parameters which may be characteristic ofthe polymer. The general concept of the ease with which a permeantpasses through a barrier is often referred to as "permeability." Thisgeneral term "permeability" does not refer to the mechanism of thepermeation but only to the rate of the transmission or transport.

Membranes of films are generally described as permeable, semi-permeable(permeable to some substances but not to others), or perm-selectivepermeable to different extents to different molecular species underequal driving force. Consequently, a given membrane may be described byany one of these terms depending upon the nature of the penetrant orpenetrants being studied (e.g., cellulose is permeable to water,perm-selective to water-glucose solutions and semi-permeable towater-protein solutions).

The terms permeability and permeability coefficient are defined invarious ways by different authors, particularly when they are involvedin different areas of research. The skilled artisan obtainingpermeability information from the literature must therefore lookcarefully at the units of the permeability constants and the method ofmeasurement. The permeability coefficient P is generally theproportionality constant between the flow of penetrant per unit area ofmembrane per unit time and the driving force per unit thickness ofmembrane. In the literature, however, one also finds flow per time, flowper area per time, or flow per area per time per unit thickness, allunder the general term permeability. In the latter cases, thepermeability coefficient may be an intrinsic property of the membrane,or it may be only a phenomenological property dependent on experimentalconditions during measurements.

For purposes of illustration in Table I below, the permeability to watervapor or, synonymously, the water vapor permeability constants of anumber of different non-edible polymer films are listed (as reported in"Permeability of Plastic Films and Coated Paper to Gases and Vapor," V.Stannett, et al., TAPPI Monograph Series No. 23, 1963, and "PolymerHandbook," H. Yasuda, and V. Stannett, John Wiley and Sons (InterscienceDivision), New York, III-229-240, 1975) and serves as a guide to thecurrent capabilities of overwrap packaging film water vaporpermeability.

                  TABLE I    ______________________________________                               Water Vapor    Film             Thickness*                               Permeability**    ______________________________________    Low density polyethylene                     .0022     7.3    High density polyethylene                     .0045     35    Polyvinylidene chloride                     .0025     0.05    (Saran)    Polyacrylonitrile                     N.A.      30    Cellulose acetate                     N.A.      680    (unplasticized)    Polystyrene      N.A.      120    Ethyl cellulose  N.A.      1200    ______________________________________     *thickness in inches     **units [cm.sup.3 (STP)cm.sup.-2 sec.sup.-1 (cmHg).sup.-1 cm ×     10.sup.-9

In the above table, while exemplary film thicknesses are given forillustration of typical use film thickness, the water vapor permeabilityvalues are intrinsic to the materials and independent of thickness.

Also for purposes of illustration, examples of several edible films notwithin the scope of the present invention comprising ordinary shellac,cellulose derivatives and/or simple mixtures thereof and other currentlyavailable food approved film formers or coatings are listed in Table IIalong with their water vapor permeability constants as determined bymethodology outlined in ASTM E96-66 (Reapproved 1972).

                  TABLE II    ______________________________________                               Water Vapor    Film             Thickness*                               Permeability**    ______________________________________    Hydroxypropyl methyl                     .002      49,280    cellulose    Hydroxypropyl cellulose                     .002      873    Zein-Corn protein                     .0004     168    Paraffin wax on citrus                     .0011      10    fruit.sup.A.B.    Shellac-bleached .0005      90    Shellac-bleached .0012      81    ______________________________________     *thickness in inches     **units [cm.sup.3 (STP)cm.sup.-2 sec.sup.-1 (cmHg).sup.-1 cm ×     10.sup.-9     .sup.A. use limited by Code of Federal Regulations (CFR) Vol. 21, 172.275     1984.     .sup.B. W. M. Miller and W. Grierson, Transactions of the ASAE, 1884-1887     1983.

Ordinary shellac and cellulose derivatives are being used increasinglyas a glaze in the pharmaceutical and confectionery industries. Thesefood grade shellacs and/or cellulose derivatives are dissolved in ethylalcohol and used for coating tablets and confections by panning,spraying, brushing or curtain coating methods. However, pure cellulosederivatives generally are poor coatings as they impart a lubrioustexture when dissolving, exhibit minimal flexibility and generally poorwater impermeable coatings.

Additionally, known coating compositions based upon pure, non-heat curedshellac suffer from other disadvantages. Noticeable off-flavors can beassociated with shellac. While these problems are of less concern in thefabrication of orally administered medicines or vitamins, such problemsare significant in other types of food products. Additionally, whileknown shellac based coatings initially offer good moistureimpermeability, such coatings tend to swell in the presence of moistureover time. As the coatings swell and absorb moisture, their barrierproperties deteriorate. Thus, there is a continuing need for improvedshellac based coating compositions with extended shelf life due todecreased susceptibility to swelling in the presence of moisture.Accordingly, it is an object of the present invention to provide ediblecoating compositions with improved moisture impermeability.

It is a further object to provide coating compositions having improvedresistance to water swelling.

Another object of the present invention is to provide coatingcompositions which contain neither non-food approved ingredients normetal salts of fatty acids.

Still another object is to provide methods for preparing such coatingscompositions.

It is an object of the present invention to provide methods forpreparing such coating compositions which can be used withheat-sensitive substrates.

It is a further object of the present invention to provide coatingcompositions having improved flavor due to masking of the off-flavorsassociated with shellac.

It has been surprisingly discovered that the above objects can berealized and superior coating compositions and coatings obtained fromcross-linked mixtures of shellac and certain edible reactants. In itsprincipal method aspect, the present invention resides in the surprisingdiscovery that coated articles, even heat sensitive articles, can beobtained with edible barriers exhibiting superior resistance to moisturemigration using the instant coating compositions.

SUMMARY OF THE INVENTION

The present invention relates to coating compositions, to coatingsprepared therefrom, to both pre-application and post-application methodsof preparation, and to coated articles fabricated from the compositions.The coated compositions are based upon heat cured or polymerizedshellac. In highly preferred embodiments, the shellac is heat cured orco-polymerized with certain edible members containing reactive hydroxylor acid moieties and provide superior coatings or barriers to moistureand oxygen penetration as well as improved resistance to moistureswelling.

The coating compositions essentially comprise a heat cured mixture of aparticularly defined shellac alone or in combination with a secondedible reactant member. The edible reactant member can be selected fromthe group consisting of edible sources of polyphenolics, edible sourcesof benzaldehyde and its derivatives, acetylated monoglycerides,polyglycerol esters, straight chain mono-carboxylic acids,monoglycerides, diacetyl tartaric acid esters of monoglycerides andmixtures thereof. The ratio of shellac to reactant member essentiallyranges from 1:0.001 to 1:1.5. In more preferred embodiments, thecoatings additionally comprise an acid catalyst. Suitable acid catalystsinclude citric, malic, hydrochloric and tartaric acids. The ratio ofacid catalyst to combined weight of shellac and reactants ranges fromabout 10 to 400:1.

The preferred method for preparing the coating compositions involvesfirstly dry blending the ingredients. Next, the blend is heated in a drystate to 130° to 175° C. for a period of 1 to 15 minutes. While molten,the heat cured composition so formed is dissolved in a food gradesolvent. The solution is then applied to a substrate and the coatedsubstrate is allowed to dry to form articles comprising the coatings ofthe present invention.

In another embodiment, the coated food articles of the present inventioncan be prepared by applying the reactants including an acid catalyst toa food substrate, preferably diluted in a food grade solvent andthereafter being dried at elevated temperatures to form a film. The filmcan range from 0.1 to 5 mil in thickness.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a table (Table IV) showing the results of testing of thewater resistance of films prepared from the present coating compositionswhich results are further described with respect to Example 22.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to edible coating compositions, to theirmethods of preparation, and to coated food products and to dry blends ofunreacted materials useful in preparing the present coatingcompositions. The coating compositions essentially comprise a shellac,specially defined polymerized alone or in combination with certainedible reactant members having reactive hydroxyl or acid moieties. Thepresent compositions are co-polymers wherein one monomer is shellacwhile a second monomer or reactant member can be selected from amongseveral classes of materials. Each of these essential and preferredcomponents as well as product preparation and use are described indetail below.

Throughout the specification and claims, percentages and ratios are byweight and temperatures in degrees Fahrenheit, unless otherwiseindicated. Molecular weights are weight average molecular weight(M_(w)), unless otherwise indicated.

First Reactant

Shellac

A particular shellac is the essential material from which the presentcoating compositions are prepared. Shellac essentially comprises about25% to 100% of the coating compositions. Better results in terms of bothlow moisture permeability and film flexibility are obtained when theshellac comprises about 50% to 99.9% of the composition. Best resultsare obtained when the shellac comprises about 58% to 99.9% of thecoating composition.

Shellac or lac is a naturally occurring resin of animal origin. Thechemical nature of shallac is still not completely understood. It isknown that shellac is a polyester type of resin formed as a naturalcondensation product of aleuritic acid (9, 10, 16-trihydroxy palmiticacid) and schellolic acid. It has free carboxyl, hydroxyl and aldehydegroups and is unsaturated. When considering the properties of shellac,it must be remembered that shellac is a natural product of animal originand differs somewhat from one source to another whether from India,Thailand or other areas.

Generally, however, shellac contains about 67.9% carbon, 9.1% hydrogenand 23.0% oxygen, corresponding to an emperical formula of (C₄ H₆O)_(n). Investigations into the molecular weight of fresh or unreactedshellac have concluded it to be about 1000. Based on this, the averageshellac molecule has an average of n=15, and ranges from n=6 to n=22 (asdescribed by W. H. Gardner, W. F. Whitmore, and H. J. Harris, Ind. Eng.Chem. 25,696(1933) and S. Basu, J. Indian Chem. Soc. 25,103(1948). Theaverage molecule contains one free acid group, three ester linkages,five hydroxyl groups and possibly a free or potential aldehyde group asindicated by acid value, hydroxyl values, saponification value andcarboxyl value determinations. Due to these groups and its chemicalnature, shellac is known to age or polymerize with itself. Uncontrolledpolymerization makes a shellac film less alcohol soluble and waterpermeable, but also undesireably increases the brittleness of a shellacfilm and lessens its usefulness as a coating.

Additionally, shellacs are commonly treated in various ways to modifyits properties. Not all shellacs used in other food applications can beused herein. It is essential to use only dewaxed, filtered, carbon blackdecolorized, non-chemically modified or "virgin" shellac. It has beensurprisingly found that other refined or bleached shellacs do notpossess the reactivity required to cross-link so as to be useful in thepresent invention. Suitable shellacs are available from commercialsuppliers such as Kane International, Larchmont, New York. Shellac canbe reacted with the to be described reactants within a broad range.Useful weight ratios of shellac to second reactant(s) range from about1:0.001 to 1:2. Better results in terms of permeability reduction,flexibility and water resistivity are obtained when the shellac tosecond reactant ranges from 1:0.001 to 0.25. Of course, the propertiesof the film materials which comprise the present compositions will varysomewhat with regard to specific values of water impermeability,flexibility, and the like depending upon selection of specific reactantmaterials or mixtures thereof and particular ratios between thereactants. However, especially with higher ratios of reactants withshellacs, minor amounts of the second reactant may not completely reactwith the shellac or even, with certain reactants, exhibit some selfcross linking.

Indeed, while the present invention is directed primarily to thesuperior coating compositions which are copolymers of the present,particularly defined shellac and a second reactant member, the skilledartisan will appreciate that useful coating compositions can be preparedwhich are monomeric polymers using the selected shellacs described abovealone.

Second Reactant

In one embodiment of the present invention, the present compositions andmethods for their preparation essentially comprise a second ediblereactant member.

The second reactant can be selected from any one of the several to-bedescribed classes of materials. Each of these classes of materials havein common the presence of species having a reactive acid or hydroxymoiety which can inter-react with the reactive moieties of shellac. Thepresent coating compositions can comprise from about 0 to 75% of thesecond reactant. For better results, the coating compositions compriseabout 0.1% to 50%.

Organic Acid

The most highly preferred class of materials which can be used as thesecond reactant to prepare the copolymer coating compositions is certainmono- and di-carboxylic organic acids. Among the important benefits fromemploying the instant organic acid adducts is that the adduct or secondreactants modestly increase the moisture impermeability of the films.Improvements in film flexibility are also obtained. Film flexibility isimportant to avoiding cracks and fissures in the film occasioned byhandling or temperature change which can result in film failure.Additionally, the organic acids in part help mask off-flavors associatedwith shellac.

Especially useful herein are all edible non-substituted mono- anddi-carboxylic acids. The skilled artisan will have no problem selectingparticular acids for use herein. Preferred reactant materials due totheir cost, flavor, availability and favorable affect on filmflexibility, water durability and permeability are selected from thegroup consisting of adipic acid, succinic acid, oleic acid, lauric acid,stearic acid and mixtures thereof. Preferred for use herein are stearicacid, lauric acid, adipic acid and mixtures thereof.

Edible Sources of Polyphenolics

A second class of materials useful herein as a second reactant is ediblesource of polyphenolics. Any of a variety of common edible food approvedmaterials can be employed as sources of polyphenolics and/or polyhydricalcohols. These materials can, for example, include plant parts,dehydrated fluid or solid extract or juices or concentrates, oils, gums,balsams, resins, oleoresins, waxes and distillates. Each material can beused alone or in combination with other edible sources of polyphenolic,tannins; both hydrolyzable and condensed, and/or polyhydric alcohols.Exemplary of the wide variety of known edible sources of polyphenolicsand/or polyhydric alcohols are cranberries, hexane extracts of blanchedor raw cashew nut meats, cassia pulp, grape skins, grape pulps, tea,coffee, hops, carob seeds and pods, soybeans, green apples, persimmons,tobacco and sorghum bran. A very large number of natural sources ofpolyphenols and tannins is given in D. K. Salunkhe, S. J. Jadhav, S. S.Kadam, J. K. Cheven, "Chemical, Biochemical, and Biological Significanceof Polyphenols in Cereals and Legumes", CRC Handbook: Critical Reviewsin Foods and Nutrition, Vol. 17, Issue 3, pp 277-305, (1982) and N. R.Reddy, M. D. Pierson, S. K. Sathe, D. K. Salunkhe, "Dry Bean Tannins: AReview of Nutritional Implications," Journal American Oil ChemistsSociety, Vol. 62, 3, 541-549, March 1985.

Edible Source of Benzaldehydes and Benzaldehyde Derivatives

Another class of materials useful herein as a second reactant is ediblesources of benzaldehydes and its derivatives. Any of a variety of commonedible food approved materials can be employed as sources ofbenzaldehydes and/or benzaldehyde derivatives. These materials can, forexample, include plant parts, dehydrated fluid or solid extracts orjuices or concentrtes, oils, gums, balsams, resins, oleoresin, waxes anddistillates. Each can be used alone or in combination with other ediblebenzaldehydes and/or benzaldehyde derivatives. Exemplary of the widevariety of known edible sources of benzaldehyde and/or benzaldehydederivatives are almonds and other nut meats, fruit pits such as prune,peach, apricot, cherry, plum or the like, cloves, vanilla beans,vanillin, anise, and numerous natural flavoring substances and/orsynethetic flavoring substances such as vanillin, ethyl vanillin,anisaldehyde and the like.

Sources of Polyglycerol Esters

Polyglycerol esters ("PGE's") can also be used as the second reactantmember. PGE's are widely used in the food art primarily as emulsifiersand are well known to the food product artisan. Polyglycerol esters inthe appropriate form (oils, distillates, solids, etc.) are used alone orin combination with other edible polyglycerol esters. The polyglycerolesters of fatty acids up to and including the decaglycerol esters areprepared from corn oil, cottonseed oil, lard, palm oil from fruit,peanut oil, safflower oil, sesame oil, soybean oil, and tallow and thefatty acids derived from these substances (hydrogenated andnon-hydrogenated) and/or oleic acid derived from tallow oil fatty acids,and/or the fatty acids derived from butter oil.

Sources of Acetylated Monoglycerides

Acetylated monoglycerides are widely used in the food art asemulsifiers. Common edible food approved sources of acetylatedmonoglycerides in any form (oils, solid, waxes, m.p. 5° C.-40` C.) canbe used alone or in combination with other edible acetylatedmonoglycerides. The edible food approved acetylated monoglycerides areprepared by the interesterification of edible fats with triacetin and inthe presence of catalytic agents that are not food additives or are notauthorized regulated additives, followed by a molecular distillation orby steam stripping; or by the direct acetylation of ediblemonoglycerides with acetic anhydride without the use of catalyst ormolecular distillation and with the removal by vacuum distillation, ifnecessary, of the acetic acid, acetic anhydride and triacetin.

Sources of Stearoyl-2-lactylates and Lactylic Esters of Fatty Acids

Edible food approved sources of stearoyl-2-lactylate are prepared by thereaction of stearic acid and lactic acid and conversion to the sodium orcalcium salts. The lactylic esters of fatty acids are prepared fromlactic acid and fatty acids and/or oleic acid derived from tall oilfatty acids. Each of these composition types can be used as the secondreactant member.

Sources of Carboxylic Acids

Common edible food approved sources of straight chain monobasiccarboxylic acids and their associated fatty acids can be used herein asthe second reactant member. These materials are manufactured from fatsand oils derived from edible sources. The edible acids are capric,caprylic, lauric, myristic, oleic, palmitic, and stearic acids as wellas margaric, arachidic, behenic and lignoceric acids.

Sources for natural edible food approved di- and tri-carboxylic acidsinclude fruit and citrus peel, pulp, juices; also, citric acid solventextraction from conventional Aspergillus niger fermentation liquor, andnumerous other natural sources.

Sources for di- and tri-carboxylic acids manufactured by synthetic meansare also acceptable provided the FDA-CFR written regulations arepracticed as to source and method of preparation.

Mono- and di-glyceride

Mono- and di-glycerides can each be used as the second reactant member.Edible food approved monoglycerides are prepared by the esterificationof fatty acids, consisting of one or any mixture of the followingstraight chain monobasic carboxylic acids and their associated fattyacids manufactured from fats and oils derived from edible sources:capric, caprylic, lauric, myristic, oleic, palmitic and stearic acids,and glycerol. The resulting product is a mixture of mono- anddi-glycerides and can be used as such as well as distilledmonoglycerides of fatty acids and combinations thereof.

Sources of Diacetyl Tartaric Acid Esters of Monoglycerides (DATEMS)

Edible food approved diacetyl tartaric acid esters of monoglycerides(DATEMS) are obtained by reacting a monoglyceride (preferablymolecularly distilled) and diacetyl tartaric acid anhydride. Thephysical properties of the DATEMS depend primarily on the type of fattyacids and the molar quantities involved. Generally, the DATEMS areliquid and/or solids at room temperature (mp. 0°-50° C.).

Optional Ingredients

A variety of optional ingredients can be added to the presentcompositions to improve one or more properties. Such adjuvants caninclude, for example, flavors, colors, vitamins and the like.Additionally, additives which reduce the growth of microorganisms can beincorporated into the described coating compositions especially when thecompositions are to be used for providing protective films on externalsurfaces. Such additives or preservatives include sorbic acid, potassiumsorbate, methyl p-hydroxybenzoate, sodium benzoate, sodium propionate,and propyl p-hydroxybenzoate. The addition of even small concentrationsof such preservatives results in a marked improvement in reducing orpreventing the growth of microorganisms. Adequate protection against thegrowth of microorganisms is obtained if the concentration of thepreservative in the coating constitutes about 0.01% to 0.2% by weight ofthe coating. In addition, suitable anti-oxidants approved for food usecan be included in the coating compositions.

Method of Preparation

The present coating compositions can be obtained by blending theunreacted components and heat curing in a dry state. The heat curing canbe practiced as convenient either before or after application to thedesired substrate. The blending can be done either by dry blending or bydissolving in a solvent and thereafter removing the solvent. The processof this invention produces a chemical union between all of the reactantswith the shellac forming an integral part of the resulting resinousmolecules.

The most highly preferred method is the pre-application curingembodiment. This method is preferred due to the realization of filmswhich are more highly water-impermeable and resistant to water swelling.The shellac alone if used by itself, or if along with the othermaterials, all the components are first dry blended to form ahomogeneous mixture. If desired, such formulated unreacted compositionscan themselves be marketed on a supplier basis. The order in which thecomponents are admixed is not critical. Thereafter, the dry blend isheated to about 130° to 175° C., preferably 138° to 150° C. for a periodof about 1 to 15 minutes to form the present heat cured coatingcompositions. Temperatures in excess of 175° C. or addition of acidcatalysts (organic or mineral) cause too rapid and uncontrollablepolymerization with the resulting material being insoluble in ethanoland other food approved solvents.

While still molten, the melt or magma is poured into a room temperaturefood grade solvent such as ethanol with agitation. If allowed to cool tosolidification, the heat cured shellac is not readily soluble. However,if desired, the cured shellac may be allowed to solidify and then bereheated as convenient for dissolution into the solvent.

An acid catalyst is undesirable in this embodiment of the method ofpreparation in contrast to the to-be-described post application curingtechnique. Indeed, excessive acidity can cause the reaction to proceedat an uncontrolled rate resulting in an unusable reaction product andthus desirably the dry mixture is substantially free of an acidcatalyst. In the undiluted form, the shellac itself has sufficientacidic character to initiate polymerization at a controllable rate uponsimple heating.

Within these reaction parameters, it is desired to produce cross-linkedshellac or copolymer having a weight average molecular weight (M_(w))ranging from about 1,500 to 6,000 as determined by gel permeationchromatography. These pre-application curing methods are particularlyuseful when coatings are desired to be applied to heat sensitivematerials, e.g., materials of low melting point ingredients and havingparticular shapes, e.g., chocolate chips. The solution may also beremoved to provide resins for the coating compositions.

The coating compositions realized herein are thermoplastic resins. Theresin compositions thus can be used for curtain-coating techniques offood coating, i.e., involving the extrusion of a sheet which is placedover the substrate with the aid of suction while still molten. Thedescribed resin coating compositions, however, are particularly suitablefor use in conventional coating techniques such as dipping, brushing orspraying. These operations can be conducted employing a melt of thecoating composition or by employing solutions thereof in food gradesolvents.

Another suitable method of preparation is to heat cure after applicationto a substrate of the reactant material(s). In this embodiment, theshellac and/or other components including acid catalyst are dissolved ina food grade solvent, e.g., ethanol, to form preferably about a 10% to20% solution which concentration includes an acid catalyst. Among foodgrade solvents, ethanol is the solvent of choice.

Shellacs are not generally readily soluble in water. However, certainammonia treated shellacs are more easily dissolved in water. Also, whenwater is sweetened with ammonia to a pH of 8.5 to 9.0, the present,particularly defined shellacs can be dissolved in the water. Modestadditions of alcohol to water can be used, if desired, to disperse themono- and di-carboxylic acid materials in the alkaline water ifemployed. The aqueous solution can be applied to a substrate and allowedto dry to form a film. If alkaline water is used as the solvent, thenthereafter, a second solution containing the acid catalyst can beapplied over the dried film of unreacted reactants. Increased amounts ofacid catalyst should be employed so as to first neutralize the residualalkalinity. Thereafter, the coated substrate can be heat treated asdescribed further below.

An edible strong acid catalyst is essentially employed in thisembodiment of forming the present coating compositions. The acidcatalyst allows for the accelerated and controlled cross-linking of theshellac. Suitable for use herein are both edible mineral and organicacids. The useful organic acid catalyst herein are distinguished fromthe above described adduct organic acid reactants principally by therelatively greater acidity of the present strong acid catalystmaterials. Exemplary materials useful herein for the acid catalystincludes citric acid, tartaric acid, phosphoric, hydrochloric acid,malic acid and mixtures thereof. Preferred for use herein are citricacid and hydrochloric acid.

The acids are used in amounts effective to promote and accelerate thecross-linking of the shellac. Since the cross-linking step is practicedin a dry state, conventional pH measurements of acidity areinappropriate. However, good results are obtained when the weight ratioof acid catalyst to the weight of shellac in the dry composition rangesfrom about 0.001 to 0.1:1. Thus, if ethanol is the solvent, the reactantsolutions from which the pre-heat cured films are prepared can containabout 0.1% to 10% of the acid catalyst member(s) and preferably 0.25% to0.5% in addition to the concentrations of shellac if used alone, or ifused in combination with a second reactant. Best results in terms ofoptimum hardness and permeability are obtained when the solutionconcentration ranges from 0.5% to 3%.

The solution is then applied by conventional techniques to a substrateto form a coated substrate and dried. The dried, coated substrate isthen heated for about 2 to 15 minutes at 130° to 180° C. to cure thecoated composition. Slightly longer heating times may be required tobring the temperature to within the above temperature range if thecoated substrate has not been completely dried prior to heating. Afterthe heat curing step, the substrate will be covered with the coatings ofthe present invention. This embodiment is particularly useful for usewith substrates which are heat tolerant, e.g., baked goods or containermaterials.

Of course, additional coat layers, e.g., second or even fifth, can beapplied to the substrate if desired to increase further the sealingproperties of the coat. The coating obtained with the described coatingcompositions are strong, highly water and oxygen impermeable, resistantto swelling, flexible and resilient even at freezer temperatures even inthe form of thin films. Continuous, pin-hole-free coatings are readilyobtained.

The optimum thickness of a coating employing the present compositionswill vary depending on the particular application involved, the degreeof protection desired, and the expected storage environment. As ageneral rule, the coating should have sufficient thickness to assure acontinuous coating and give the desired degree of protection, andwhether or not it is desirable for the barrier not to be readilyapparent. Good sealing protection can be achieved with a coatingthickness as thin as 0.1 mil. Greater protection, while nonethelessbeing organoleptically acceptable, can be provided by films up to about5 mil in thickness. Preferred thicknesses range from about 0.25 to 2mil.

The coating compositions can be used on all manner of substrates used inconnection with food products whether non-edible, e.g., on containers,sticks and the like, or edible substrates, e.g., fruits, vegetables,meats, candies, tablets for oral use and the like. The present coatingcompositions find particular usefulness as barriers in composite foodproducts having a first food phase or region of one material and asecond phase or region of a second material. For example, pieces ofsoft, moist cheese may be coated with the present film coat andsandwiched between dry cracker slices to provide conventionally packagedsnacks which are not subject to staling as quickly by moisture migrationor other interaction between the cheese and cracker. Surprisingly, thepresent coatings find even greater usefulness with high moisture, frozenor chilled food products such as ice cream sandwiches or cookies andfruit (both pieces and jams, jellies and preserves) or chocolate chipsand dairy products.

The claims and the specification describe the invention presented, andthe terms that are employed in the claims draw their meaning from theuse of such terms in the specification. Some terms employed in the priorart may be broader in meaning than specifically employed herein.Whenever there is a question between the broader definition of such termas used in the prior art and the more specific use of the term herein,the more specific meaning is meant.

The invention is further illustrated by the following examples.

EXAMPLE 1

Forty grams of dewaxed, carbon filtered shellac and 5.0 grams of stearicacid were dissolved in 200 ml 95% ethanol and warmed slightly to about125° F. to effect solution with stirring. Upon complete solution, 5 mlof a concentrated citric acid solution (35 g in 80 ml 95% ethanol) wasadded. The solution was spread on teflon, glass and vegetable papersubstrates and heat cured at 300° F. (150° C.) for 10 minutes. Theresulting film was water resistant, exhibited no water swelling and nostess cracking when flexed. The coating was tough, abrasion resistantand visibly free from defects.

EXAMPLE 2

Forty grams of dewaxed, carbon filtered shellac and 2.1 grams ofsuccinic acid were dissolved in 200 ml 95% ethanol and warmed slightlyto about 125° F. to effect solution with stirring. Upon completesolution, 0.2 grams concentrated HCl in 10 ml 95% ethanol was added. Thesolution was spread on teflon, glass and vegetable paper substates andheat cured at 300° F. (150° C.) for 10 minutes. The resulting film waswear resistant, exhibited no water swelling and no stress cracking whenflexed. The coating was abrasion resistant, tough and visibly free fromdefects.

EXAMPLE 3

Forty grams of dewaxed, carbon filtered shellac and 14.1 grams of lauricacid were dissolved in 200 ml of 95% ethanol and warmed slightly toabout 125° F. (51° C.) to effect solution with stirring. Upon completesolution, 5 ml of a concentrated citric acid solution (35 g in 80 ml 95%ethanol) was added. The solution was spread on one-half of a baked sugarwafer and heat cured at 300° F. (150° C.) for 10 minutes. The resultanttreated half wafer appeared glazed and possessed a tough hard coating,the untreated half wafer appeared normal in every respect--no glaze andno tough hard coating. Small water droplets were placed on both thetreated and untreated wafer. The droplets on the unteated surfaceingressed immediately into the wafer substrate with subsequent softeningof the water, while the treated surface droplets evaporated (about 10+minutes) before any degradation of the resultant coating was evident.The coating on the wafer gave no off taste with respect to the untreatedside and also exhibited significant moisture resistance.

EXAMPLE 4

Forty grams of dewaxed, carbon filtered shellac and 5.0 grams of stearicacid were placed in an oil jacketed heating vessel along with 5 ml of aconcentrated citric acid solution (35 g in 80 ml 95% ethanol) and heatedto 135° C. The magma or molten mixture immediately stiffened, becameunstirrable, and would not disolve into a 10:1 mixture of ethanol (95%)and ethylacetate.

EXAMPLE 5

Forty grams of dewaxed, carbon filtered shellac and 12.5 grams ofstearic acid were placed in an oil jacketed heating vessel and heated to135° C. Upon reaching temperature the magma began to foam and thereaction was run for eight minutes with stirring. The magma or moltenmixture was somewhat fluid with a final temperature of 140° C. Themolten mixture was poured into 900 ml of a 10:1 mixture of 95% ethanoland ethylacetae with high shear mixing and upon solution was diluted toone liter. The resulting film was hard, glossy, continuous, abrasion andwater resistant.

EXAMPLE 6

One hundred grams of dewaxed, carbon filtered shellac and 2.7 grams ofdecaglycerol monooleate were placed in an oil jacketed heating vesseland heated to 138° C. The reaction was run for 7.5 minutes withstirring. The magma or molten material was stiff with a finaltemperature of 148° C. The molten material was poured into 900 ml of a10:1 mixture of 95% ethanol and ethylacetate with high shear mixing andupon solution was diluted to one liter.

EXAMPLE 7

One hundred grams of dewaxed, carbon filtered shellac and 3.4 grams ofvanillin were placed in an oil jacketed heating vessel and heated to138° C. Upon reaching temperature the magma or molten mixture began tofoam and the reaction was run for seven minutes with stirring. The magmawas somewhat stiff with a final temperature of 147° C. The moltenmixture was poured into 900 ml of a 10:1 mixture of 95% ethanol andethylacetate with high shear mixing and upon solution was diluted to oneliter.

EXAMPLE 8

One hundred grams of dewaxed, carbon filtered shellac and 5.0 grams ofacetylated monoglycerides (90-100% acetylated) were placed in an oiljacketed heating vessel and heated to 138° C. Upon reaching temperaturethe magma or molten mixture began to foam and the reaction was run for7.5 minutes with stirring. The magma was stiff with a final temperatureof 148° C. The molten mixture was poured into 900 ml of a 10:1 mixtureof 95% ethanol and ethylacetate with high shear mixing and upon solutionwas diluted to one liter.

EXAMPLE 9

1080 grams of dewaxed, carbon filtered shellac and 120 grams of stearicacid were placed in an oil jacketed heating vessel and heated to 135° C.Upon reaching temperature the magma or molten mixture began to foam andthe reaction was run for eight minutes with stirring. The magma wassomewhat fluid with a final temperature of 142° C. The molten mixturewas poured into 900 ml of a 10:1 mixture of 95% ethanol and ethylacetatewith high shear mixing and upon solution was diluted to one liter.

EXAMPLE 10

One hundred grams of dewaxed, carbon filtered shellac and 3.4 grams oftannic acid were placed in an oil jacketed heating vessel and heated to138° C. Upon reaching temperature the magma or molten mixture began tofoam and the reaction was run for eight minutes with stirring. The magmawas stuff and grainy with a final temperature of 147° C. The moltenmixture was poured into 900 ml of a 10:1 mixture of 95% ethanol andethylacetate with high shear mixing and upon solution was diluted to oneliter.

EXAMPLE 11

One hundred grams of dewaxed, carbon filtered shellac and 3.7 grams ofanisaldehyde were placed in an oil jacketed heating vessel and heated to135° C. Upon reaching temperature the magma or molten mixture began tofoam and the reaction was run for nine minutes with stirring. The magmawas soft and fluid with a final temperature of 148° C. The moltenmixture was poured into 900 ml of a 10:1 mixture of 95% ethanol andethylacetate with high shear mixing and upon solution was diluted to oneliter.

EXAMPLE 12

One hundred grams of dewaxed, carbon filtered shellac and 3.2 grams ofoleic acid were placed in an oil jacketed heating vessel and heated to140° C. Upon reaching temperature the magma or molten mixture began tofoam and the reaction was run for 8.5 minutes with stirring. The magmawas soft and fluid with a final temperature of 148° C. The moltenmixture was poured into 900 ml of a 10:1 mixture of 95% ethanol andethylacetate with high shear mixing and upon solution was diluted to oneliter.

EXAMPLE 13

One hundred grams of dewaxed, carbon filtered shellac and 1.3 grams ofstearic acid were placed in an oil jacketed heating vessel and heated to140° C. Upon reaching temperature the magma or molten mixture began tofoam and the reaction was run for 8.5 minutes with stirring. The magmawas moderately soft and fluid with a final temperature of 148° C. Themolten mixture was poured into 900 ml of a 10:1 mixture of 95% ethanoland ethylacetate with high shear mixing and upon solution was diluted toone liter.

EXAMPLE 14

One hundred grams of dewaxed, carbon filtered shellac was placed in anoil jacketed heating vessel and heated to 140° C. Upon reachingtemperature the magma or molten mixture began to foam and the reactionwas run for eight minutes with stirring. The magma was stiff andflowable with a final temperature of 150° C. The molten mixture waspoured into 900 ml of a 10:1 mixture of 95% ethanol and ethylacetatewith high shear mixing and upon solution was diluted to one liter.

EXAMPLE 15

One hundred grams of dewaxed, carbon filtered shellac and 3.3 grams oftartaric acid were placed in an oil jacketed heating vessel and heatedto 138° C. Upon reaching temperature the magma or molten mixture beganto foam and the reaction was run for eight minutes with stirring. Themagma was grainy and stiff with a final temperature of 148° C. Themolten mixture was poured into 900 ml of a 10:1 mixture of 95% ethanoland ethylacetate with high shear mixing and upon solution was diluted toone liter.

EXAMPLE 16

One hundred grams of dewaxed, carbon filtered shellac and 3.3 grams ofsuccinic acid were placed in an oil jacketed heating vessel and heatedto 140° C. Upon reaching temperature the magma or molten mixture beganto foam and the reaction was run for 8.5 minutes with stirring. Themagma was moderately stiff with a final temperature of 148° C. Themolten mixture was poured into 900 ml of a 10:1 mixture of 95% ethanoland ethylacetate with high shear mixing and upon solution was diluted toone liter.

EXAMPLE 17

One hundred grams of dewaxed, carbon filtered shellac and 4.1 grams ofdistilled monoglycerides were placed in an oil jacketed heating vesseland heated to 138° C. Upon reaching temperature the magma or moltenmixture began to foam and the reaction was run for 8.5 minutes withstirring. The magma was soft and flowable with a final temperature of148° C. The molten mixture was poured into 900 ml of a 10:1 mixture of95% ethanol and ethylacetate with high shear mixing and upon solutionwas diluted to one liter.

EXAMPLE 18

One hundred grams of dewaxed, carbon filtered shellac and 3.6 grams ofdiacetyl tartaric acid esters of monoglycerides were placed in an oiljacketed heating vessel and heated to 138° C. Upon reaching temperaturethe magma or molten mixture began to foam and the reaction was run fornine minutes with stirring. The magma was moderately stiff with a finaltemperature of 147° C. The molten mixture was poured into 900 ml of a10:1 mixture of 95% ethanol and ethylacetate with high shear mixing andupon solution was diluted to one liter.

EXAMPLE 19

One hundred grams of dewaxed, carbon filtered shellac and 3.2 grams ofstearoyl-2-lactylate were placed in an oil jacketed heating vessel andheated to 138° C. Upon reaching temperature the magma or molten mixturebegan to foam and the reaction was run for nine minutes with stirring.The magma was moderately stiff with a final temperature of 147° C. Themolten mixture was poured into 900 ml of a 10:1 mixture of 95% ethanoland ethylacetate with high shear mixing and upon solution was diluted toone liter.

EXAMPLE 20

Forty grams of dewaxed, carbon filtered shellac and 56.5 grams of lauricacid were placed in an oil jacketed heating vessel and heated to 135° C.Upon reaching temperature the magma or molten mixture began to foam andthe reaction was run for fifteen minutes with stirring. The magma wasfluid and pourable with a final temperature of 148° C. The moltenmixture was poured into 900 ml of a 10:1 mixture of 95% ethanol andethylacetate with high shear mixing and upon solution was diluted to oneliter.

EXAMPLE 21

One hundred grams of dewaxed, carbon filtered shellac and 25.8 grams ofcranberry concentrate were placed in an oil jacketed heating vessel andheated to 138° C. Upon reaching temperature the magma or molten mixturebegan to foam and the reaction was run for nine minutes with stirring.The magma was soft and fluid with a final temperature of 146° C. Themolten mixture was poured into 900 ml of a 10:1 mixture of 95% ethanoland ethylacetate with high shear mixing and upon solution was diluted toone liter.

EXAMPLE 22

One hundred grams of dewaxed, carbon filtered shellac and 5.6 grams ofcashew nut oil-hepane extract were placed in an oil jacketed heatingvessel and heated to 137° C. Upon reaching temperature the magma ormolten mixture began to foam and the reaction was run for nine minuteswith stirring. The magma was moderately hard and fluid with a finaltemperature of 149° C. The molten mixture was poured into 900 ml of a10:1 mixture of 95% ethanol and ethylacetate with high shear mixing andupon solution was diluted to one liter.

The water vapor permeabilities of the edible films prepared as in theabove examples as well as pure un-heat cured shellac have the valuesprovided in Table III as follows:

                  TABLE III    ______________________________________    WATER VAPOR PERMEABILITIES    FOR SHELLAC FILMS    FILM COMPOSITION                   H.sub.2 O VAPOR PERMEABILITY*    ______________________________________    shellac-unbleached-                   20    unreacted    Example     1             2.3     2             1.3     3             N.A.     4             N.A.     5             0.41     6             15.2     7             7.6     8             6.8     9             0.88    10             2.5    11             3.3    12             3.1    13             3.5    14             1.8    15             4.2    16             3.8    17             1.8    18             2.0    19             2.1    20             0.42    21             0.97    22             1.3    ______________________________________     *cm.sup.3 (SPT)cm.sup.-2 sec.sup.-1 cmHg.sup.-1 cm × 10.sup.-8

The values given in Table III above indicate that compared to untreatedshellac the present films exhibit superior resistance to moisturepermeability.

The increased resistance of these prepared films as in the above exampleas well as bleached shellac to water swelling is provided in Table IV asfollows:

TABLE IV

The values given in Table IV indicate that when compared to conventionalbleached shellac, the present films exhibit superior resistance to waterswelling.

The increase in both weight average (M_(w)) and number average (M_(n))molecular weights and the increased narrowness of the molecular weightdistribution (M_(w) /M_(n)) of the prepared films in the examples ascompared to the unheated shellac samples is evident as shown in Table Vas follows:

                  TABLE V    ______________________________________    FILM COATING MOLECULAR    WEIGHT DISTRIBUTION.sup.A                  FILM COMPOSITION     Unreacted Shellac                    M.sub.w M.sub.n                                   M.sub.w /M.sub.n                                           M.sub.z    ______________________________________    Shellac 56 SONNE (pale)                     821     152   5.39    3083    Shellac 58 KOMET (amber)                    1023     204   5.01    2824    Shellac 60 PRIMA (orange)                     571     149   3.82    2269    Example     7              2639    1131   2.33    5999     8              3316    1419   2.33    7009     9              2168    1159   1.87    4356    10              3194    1205   2.65    14645    14              1910     961   1.99    4275    15              2867    1232   2.33    6786    18              1755     848   2.07    4391    ______________________________________     M.sub.w, weight average molecular weight; M.sub.n, number average     molecular weight,     M.sub.w /M.sub.n, molecular weight distribution, M.sub.z, z average     molecular weight;     .sup.A Determination using a Waters 150C ALC/GPC, mcresol at 110°     C. on a microstyragel columns (1.0E5, 1.0E4 and 1.0E3 Angstrom), flow rat     1.0 ml/min, 150 uL sample injection (0.05 g sample in 10.0 ml mcresol).     Data reduction using a Nelson Analytical Model 444 Chromatography Data     System with a GPC software package. Standardized with a series of narrow     dispersity anionically polymerized polystyrene standards (Waters     Associates).

The effect of molecular weight or molecular weight distribution onpolymer properties (as described by E. A. Collins, J. Bares, and F. W.Billmeyer, Jr., Experiments in Polymer Science, Wiley, New York, 1973,p. 312) are indicated in Table VI below.

                  TABLE VI    ______________________________________    EFFECT OF MOLECULAR WEIGHT OR MOLECULAR    WEIGHT DISTRIBUTION ON POLYMER PROPERTIES                                Narrow the Mole-                  Increased Mole-                                cular Weight                  cular Weight  Distribution    Polymer Properties                  (M.sub.w)     (M.sub.w /M.sub.n)    ______________________________________    Tensile Strength                  +             +    Elongation    +             -    Yield Strength                  +             -    Toughness     +             +    Brittleness   +             -    Hardness      +             -    Abrasion Resistance                  +             +    Softening Temperature                  +             +    Melt Viscosity                  +             +    Adhesion      -             -    Chemical Resistance                  +             +    Solubility    -             0    ______________________________________     +, property goes up     -, property goes down     0, little change

It is clearly evident that these above prepared films are superior inevery desirable polymer property as supported by the data in Tables IIIand IV when compared to the untreated shellac films.

What is claimed is:
 1. A method for preparing an edible, low water vaporpermeable film, comprising the steps of:A. providing a solutionconsisting essentially of
 1. a first reactant comprising a dewaxedfiltered, carbon black deodorized decolorized virgin shellac,2. anedible acid catalyst selected from the group consisting of citric,tartaric, phosphoric, hydrochloric, malic and mixtures thereof, and 3.an edible solvent;wherein the first reactant comprises about 1% to 30%by weight of the solution, wherein the acid catalyst comprises about0.1% to 10% of the solution, B. applying the solution to a substrate toform a coated substrate; and C. heating the coated substrate at atemperature of about 130° to 175° C. for about 2 to 15 minutes wherebythe solvent is evaporated to form a heat cured, polymeric, edible filmhaving an average molecular weight of at least 1,500.
 2. The method ofclaim 1 wherein the solution additionally comprises:3. a second reactanthaving a reactive hydroxyl or acid moiety selected from the groupconsisting of:a. edible sources of polyphenolics, b. edible sources ofbenzaldehyde derivatives, c. polyglycerol esters, d. edible mono- anddi-carboxylic acids, e. acetylated monoglycerides, f. diacetyl tartaricacid esters of monoglycerides, g. lactylic esters of fatty acids, h.mono- and di-glycerides, and mixtures thereof; wherein the weight ratioof shellac to second reactant ranges from about 1:0.001 to 1:1.5,wherein the combined concentration of shellac and second reactant in thesolution ranges from about 1% to 30% by weight.
 3. The method of claim 2wherein the weight ratio of shellac to the second reactant ranges fromabout 1:0.001 to 0.1.
 4. The method of claim 3 wherein the weight ratioof shellac to the second reactant ranges from about 1:0.01 to 0.1. 5.The method of claim 4 wherein the film ranges from about 1 to 5 mil inthickness.
 6. The method of claim 5 wherein the second reactant is anedible source of polyphenolics.
 7. The method of claim 5 wherein thesecond reactant is an edible source of benzaldehyde derivatives.
 8. Themethod of claim 5 wherein the second reactant is a polyglycerol ester.9. The method of claim 5 wherein the second reactant is an edible mono-or di-carboxylic acid.
 10. The method of claim 5 wherein the secondreactant is an acetylated monoglyceride.
 11. The method of claim 5wherein the second reactant is a diacetyl tartaric acid ester ofmonoglycerides.
 12. The method of claim 5 wherein the second reactant isa lactylic ester of fatty acids.
 13. The method of claim 5 wherein thesecond reactant is a mono- or di-glyceride.
 14. A method for preparing asubstrate coated with an edible film of low moisture permeabilitycomprising:A. heating a dry mixture consisting essentially of a refined,carbon filtered, unbleached edible shellac to a temperature of about130° to 175° C. for a period of about 2 to 15 minutes, to form across-linked polymeric shellac coating composition having an averagemolecular weight of at least 1,500, B. dissolving with agitation thecoating composition while still molten in a food grade solvent to form asolution, C. applying the solution to a substrate to form a coatedsubstrate; and D. drying the coated substrate.
 15. The method of claim14 wherein the dry mixture additionally includes,a second member havinga reactive hydroxyl or acid moiety selected from the group consistingof:a. edible sources of polyphenolics, b. edible sources of benzaldehydederivatives; c. polyglycerol esters, d. edible mono- and di-carboxylicacids, e. acetylated monoglycerides, f. diacetyl tartaric acid esters ofmonoglycerides, g. lactylic esters of fatty acids, h. mono- anddi-glycerides, and mixtures thereof; wherein the weight ratio of shellacto second member ranges from about 1:0.001 to 1:1.5.
 16. The method ofclaim 15 wherein the coating has a thickness of about 0.1 to 5 mil. 17.The method of claim 16 wherein the coating has a thickness of about 0.25to 2 mil.
 18. The method of claim 17 wherein the first reactant memberis an edible source of polyphenolics.
 19. The method of claim 17 whereinthe first reactant member is an edible source of benzaldehydederivatives.
 20. The method of claim 17 wherein the first reactantmember is a polyglycerol ester.
 21. The method of claim 17 wherein thefirst reactant member is an edible mono- or di-carboxylic acid.
 22. Themethod of claim 17 wherein the first reactant member is an acetylatedmonoglyceride.
 23. The method of claim 17 wherein the first reactantmember is diacetyl tartaric acid ester of monoglycerides.
 24. The methodof claim 17 wherein the first reactant member is a lactylic ester offatty acids.
 25. The method of claim 17 wherein the first reactantmember is a mono- and di-glyceride.
 26. The method of claim 1 whereinthe solvent comprises ethanol and wherein the film has an averagemolecular weight ranging from about 1,500 to 6,000.
 27. The method ofclaim 1 wherein the solvent comprises water having a ph of at least 8.5.28. The method of claim 26 wherein the solvent additionally comprisesethyl acetate.
 29. The method of claim 26 wherein the acid catalyst iscitric acid.
 30. The method of claim 17 wherein the solvent comprisesethanol and wherein the film has an average molecular weight rangingfrom about 1,500 to 6,000.
 31. The method of claim 30 wherein thesolvent comprises water having a ph of at least 8.5.
 32. The method ofclaim 30 wherein the solvent additionally comprises ethyl acetate. 33.The method of claim 30 wherein the acid catalyst is citric acid.